1. Field of the Invention
This invention relates to integrated circuit (IC) packaging technology, and more particularly, to an externally-embedded heat-dissipating device which is designed for use with a BGA (Ball Grid Array) IC package for dissipating the IC-produced heat during operation to the atmosphere.
2. Description of Related Art
The BGA IC packaging technology allows the IC package to be made very small in height while nevertheless incorporating a large packing density of transistor elements with a large number of I/O pins. During the operation of the internal circuitry of the IC package, a large amount of heat can be generated due to the flowing of electricity through the transistor elements on the IC chip. If this heat is not dissipated, it can cause damage to the internal circuitry of the IC chip. Therefore, it is required to provide heat-dissipating means on the IC package for heat dissipation during operation.
Types of BGA IC packages include PBGA (Plastic BGA), and TBGA (Tape BGA), which are so named in terms of the material being used to form the substrate. These BGA IC packages, however, are poor in heat-dissipating efficiency since plastics, and tape are poor in heat conductivity. To allow BGA IC packages to have a high heat-dissipating efficiency, a conventional solution is to provide a heat sink or a heat slug.
FIG. 13 is a schematic sectional diagram of a BGA IC package installed with a conventional heat-dissipating device. As shown, the BGA IC package includes an encapsulant 110, a substrate 120, and an IC chip 130 which is attached on the substrate 120 by means of silver paste 140 and is electrically connected to the substrate 120 via a plurality of gold wires 150. In addition, this BGA IC package is embedded with a thermally-conductive piece 100 in the encapsulant 110. The thermally-conductive piece 100 has a support portion 101 formed in such a manner that it can support the main body of the thermally-conductive piece 100 in an overhead manner above the IC chip 130. In the manufacture of this BGA IC package, the die-bonding process and the wire-bonding process are performed first; and after the gold wires 150 are readily bonded, the thermally-conductive piece 100 is attached onto the substrate 120 by means of an adhesive 160. After this, a molding process is performed to form the encapsulant 110 to encapsulate the IC chip 130, the gold wires 150, and the thermally-conductive piece 100, while exposing the top surface 102 of the thermally-conductive piece 100 to the outside of the encapsulant 110 so that the thermally-conductive piece 100 can come into touch with the atmosphere.
Typically, the IC chip 130 has a thickness of a=0.33 mm (millimeter); the thermally-conductive piece 100 has a thickness of c=0.3 mm; and the encapsulant 110 has a thickness of D=1.17 mm. Therefore, the bottom side of the thermally-conductive piece 100 is separated from the top side of the IC chip 130 by a distance of b=Dxe2x88x92axe2x88x92c=1.17xe2x88x920.3xe2x88x920.33=0.54 mm. This shows that the heat produced in the IC chip 130 during operation will be conducted through this 0.54 mm part of the encapsulant 110 to the thermally-conductive piece 100 where the heat can be more rapidly dissipated to the atmosphere since the thermally-conductive piece 100 has better thermal conductivity than the encapsulant 110. Compared to a BGA IC package without such a heat-dissipating device, the top side of the IC chip 130 is separated from the top side of the encapsulant 110 by a distance of b+c=Dxe2x88x92a=1.17xe2x88x920.33=0.84 mm; and therefore, the IC-produced heat will be conducted entirely through a 0.84 mm part of the encapsulant 110 to the atmosphere. From experimentation, it shows that the heat-dissipating device depicted in FIG. 13 can help increase the heat-dissipation efficiency by a factor of from 10% to 20% as compared to a BGA IC package without the heat-dissipating device.
FIG. 14 is a schematic sectional diagram of a BGA IC package installed with a modified heat-dissipating device that can help further increase heat-dissipation efficiency. As shown, the thermally-conductive piece shown in FIG. 13 is here modified in such a manner that it is formed with a downward-protruded portion 103xe2x80x2 so as to further reduce the heat path between the IC chip 130xe2x80x2 and the thermally-conductive piece 100xe2x80x2.
The foregoing two kinds of heat-dissipating devices shown in FIGS. 13 and 14, however, would cause the following drawbacks.
First, the mounting of these two conventional heat-dissipating devices on the substrate would require precise positioning so as to prevent the IC chip and gold wires from being damaged thereby. Moreover, an additional baking process is required to allow these two kinds thermally-conductive pieces to be securely fixed in position in the encapsulant, thus undesirably increasing the cycle time and complexity of the manufacture process, making the manufacture not very cost-effective.
Second, these two conventional heat-dissipating devices would be easily subjected to delamination off the encapsulant due to the fact that they are made from a thermally-conductive material with a high coefficient of thermal expansion (CTE), typically from 16 ppm/xc2x0 C. to 17 ppm/xc2x0 C., while the encapsulant has a CTE of only about 13 ppm/xc2x0 C. This CTE difference would cause the delamination whenever the package structure undergoes a cooling process subsequent to a high-temperature treatment as solder reflow or reliability test during temperature cycle. When delamination occurs, it would make the finished package poor in quality.
Third, these two conventional heat-dissipating devices would cause undesired popcorn effect during the molding process due to the reason that the support portions thereof would cause disturbance to the flowing resin used in the molding process and thus cause the undesired forming of voids in the resultant encapsulant. During the molding process, the solder reflow would easily cause the air within these voids to explode.
Fourth, these two conventional heat-dissipating devices would take up much layout space over the substrate, making the overall package configuration less compact in size and therefore unsuitable for use with the MCM (Multi-Chip Module) type of BGA IC packages.
Fifth, these two conventional heat-dissipating devices would easily cause the flowing resin used in the molding process to flash. This is because that these two conventional heat-dissipating devices are typically formed through a stamping process, which would easily cause the corners thereof to be rounded, thus allowing the flowing resin to easily pass through the rounded corners to the exposed surface. In addition, the flashed resin would make the exposed surface of the heat-dissipating device to be unplanarized, resulting in a less effective coupling of the heat-dissipating device to external heat-dissipation means. The flashed resin can be removed through sanding or laser, but such post-treatment would degrade the outer appearance of the package configuration and make the overall manufacture process more complex, and is therefore undesired.
It is therefore an objective of this invention to provide an externally-embedded heat-dissipating device for BGA IC package, which can help reduce manufacture cycle time and cost while nevertheless providing a heat-dissipation efficiency.
It is another objective of this invention to provide an externally-embedded heat-dissipating device for BGA IC package, which can help prevent delamiantion so that the manufactured BOA IC package can be assured in quality.
It is still another objective of this invention to provide an externally-embedded heat-dissipating device for BGA IC package, which can help prevent the forming of voids in the encapsulant and thus prevent the undesired popcorn effect during the molding process.
It is yet another objective of this invention to provide an externally-embedded heat-dissipating device for BGA IC package, which takes up only a small area of the layout space on the substrate so that the overall package configuration can be made more compact.
It is still yet another objective of this invention to provide an externally-embedded heat-dissipating device for BGA IC package, which can help prevent the flash of flowing resin used in the molding process, so that it would be unnecessary to use sanding or laser means to remove flashed resin and thus allow the manufactured BGA IC package to be more assured in quality.
In accordance with the foregoing and other objectives, the invention proposes an improved heat-dissipating device for BGA IC package. The heat-dissipating device of the invention comprises embedding means formed in a surface of the encapsulant and at a proximate position to the IC chip; and a thermally-conductive piece accommodated in the embedding means, which has a first surface facing against the IC chip and a second surface exposed to the outside of the encapsulant. The embedding means is a recess predefined to be formed in the encapsulant during the molding process, and which can be formed by predefining a protruded portion on a mold used to form the encapsulant so that the recess can be readily formed during the molding process.
By the invention, the overall process for manufacturing the BGA IC package can be significantly reduced in complexity since it requires no premounting and baking of the heat-dissipating device as in the case of the prior art.
Moreover, since a thermally-conductive paste is used to adhere the heat-dissipating device of the invention to the encapsulant, it can act as a cushion to help prevent delamination of the heat-dissipating device from the encapsulant.
Furthermore, since the heat-dissipating device of the invention is externally embedded, without having to use support portions to be supported on the substrate, it would not cause disturbance to the flowing resin used in the molding process, making the resulted BGA IC package more assured in quality. In addition, since the heat-dissipating device of the invention would not occupy any layout space over the substrate, the BGA IC package can be made more compact.
Still moreover, since the mounting of the heat-dissipating device of the invention is carried out after the BGA IC package is completed, it can help prevent the occurrence of flash of the flowing resin used in the molding process.
Finally, the heat-dissipating device of the invention can provide the foregoing benefits but nevertheless allowing the heat-dissipation efficiency to be better than the prior art. The invention is also more advantageous to use when mounted on an MCM type of BGA IC package than the prior art.